JPH06291585A - Surface acoustic wave element and filter - Google Patents

Abstract

PURPOSE:To provide a surface acoustic wave element having the characteristic of a low insertion loss for one direction, and a wide band characteristic. CONSTITUTION:The surface acoustic wave element in which an interdigital electrode having a thickness is provided on a piezoelectric or electrostrictive substrate 1, is equipped with a first interdigital electrode which excites a surface acoustic wave in which positive and negative electrodes 4 and 5 whose electrode width and period are gradually shortened in the transmitting direction of the surface acoustic wave are alternatively arranged, and a second interdigital electrode which receives the surface acoustic wave in which positive and negative electrodes 6 and 7 whose electrode width and cycle are gradually lengthened in the transmitting direction of the surface acoustic wave are alternately arranged. Also, this element is equipped with a third interdigital electrode which excites the surface acoustic wave in which the positive and negative electrodes whose electrode width and cycle are gradually shortened in the transmitting direction of the surface acoustic wave are alternately arranged, and a fourth interdigital electrode which receives the surface acoustic wave in which the positive and negative electrodes whose electrode width and period are gradually shortened in the transmitting direction of the surface acoustic wave are alternately arranged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave element in which a surface acoustic wave converter is provided which is provided with interdigital transducers having different electrode widths and periods in the propagation direction of the surface acoustic wave, and such a surface acoustic wave. The present invention relates to a filter using an element.

[0002]

2. Description of the Related Art Conventionally, a surface acoustic wave converter having a comb-shaped electrode composed of positive and negative electrodes provided on a piezoelectric substrate (including a piezoelectric thin film substrate) or an electrostrictive substrate generally has an equi-periodic structure. The electrodes were arranged. FIG. 4A is a plan view showing a filter using a conventional surface acoustic wave converter,
FIG.4 (b) shows the XY sectional view. 41 is a surface acoustic wave converter on the excitation side for converting an electric signal into a surface acoustic wave, 4
Reference numeral 2 denotes a receiving surface acoustic wave converter that detects the surface acoustic wave generated by the surface acoustic wave converter 41 and progressing as shown by an arrow A, and extracts the surface acoustic wave as an electric signal. Surface acoustic wave converter 4
Each of the interdigital electrodes 1 and 42 has an electrode arrangement structure with an equal period. That is, when the electrode width of the interdigital transducer is m and the period is p, p is constant and m / p is a constant (mostly "0.5").

In the surface acoustic wave converter having such an electrode arrangement structure of equal period, the generated surface acoustic waves propagate in the left and right directions with substantially the same amplitude. Therefore, it can be said that they have similar insertion loss characteristics in both directions, that is, they have bidirectional characteristics.

On the other hand, as a technique for obtaining a unidirectional surface acoustic wave converter having a characteristic of low insertion loss in only one direction by using a surface acoustic wave converter having an electrode arrangement structure of equal periods,
Conventionally, for example, a method of using a 120-degree phase shifter, a method of using a 90-degree phase shifter, and an internal reflection type unidirectionality that obtains a unidirectional characteristic by arranging reflective electrodes asymmetrically between positive and negative electrodes at equal intervals There was a method such as a converter.

Further, one of the surface acoustic wave devices is a dispersion type delay line (chirp filter). FIG. 5 is a plan view showing the structure of a conventional distributed delay line. Reference numeral 51 is a surface acoustic wave converter on the excitation side for converting an electric signal into a surface acoustic wave.
Is a surface acoustic wave converter on the receiving side that detects the surface acoustic wave generated by the surface acoustic wave converter 51 and has proceeded as shown by arrow B, and extracts it as an electric signal. Surface acoustic wave converter 52
The interdigital transducer has a positive electrode 53 and a negative electrode 54 so that the period becomes gradually shorter along the propagation direction B of the surface acoustic wave.
It has a structure in which are alternately arranged. By arranging the positive and negative electrodes in this way, the characteristic that the delay time changes in proportion to the frequency can be obtained.

[0006]

A surface acoustic wave converter having an electrode arrangement structure with an equal period has a bidirectional characteristic, and a characteristic of low insertion loss in only one direction cannot be obtained. Also,
In the technique for obtaining the above-mentioned unidirectional surface acoustic wave converter, a characteristic that the insertion loss is low in one direction is obtained, but since the surface acoustic wave converter having the electrode arrangement structure of an equal period is used, Broadband characteristics cannot be obtained.

Further, in the distributed delay line as shown in FIG. 5, the delay time of a high frequency signal is long and the delay time of a low frequency signal is a short up-chirp delay line. You can also get However, also in this case, the conventional distributed converter, that is, the converter having the bidirectional characteristic is used, and the converter is not a low insertion loss converter.

In view of the problems in the above-mentioned conventional example, the present invention has a characteristic of low insertion loss in one direction,
Another object of the present invention is to provide a surface acoustic wave device having wide band characteristics.

[0009]

In order to achieve the above object, the present invention provides a surface acoustic wave device having a comb-shaped electrode having a thickness on a piezoelectric or electrostrictive substrate.
A first interdigital transducer that excites a surface acoustic wave in which positive and negative electrodes are alternately arranged whose electrode width and period are gradually shortened in the surface acoustic wave propagation direction, and the electrode width and the electrode width gradually increase in the surface acoustic wave propagation direction. It is characterized by comprising a second interdigital transducer for receiving surface acoustic waves in which positive and negative electrodes having a long period are alternately arranged.

Further, according to the present invention, in a surface acoustic wave element in which a comb-shaped electrode having a thickness is provided on a piezoelectric or electrostrictive substrate, the electrode width and period are gradually shortened in the propagation direction of the surface acoustic wave. A third interdigital transducer that excites a surface acoustic wave in which positive and negative electrodes are alternately arranged, and a surface acoustic wave in which positive and negative electrodes whose electrode width and period are gradually shortened in the propagation direction of the surface acoustic wave are alternately arranged. And a fourth interdigital transducer for receiving.

When the electrode width of the interdigital transducer is m and the period is p, the third interdigital electrode has 0.2 ≦ m / p ≦ 0.
7 and the fourth interdigital transducer is 0.72 ≦ m / p ≦
It is preferably set to 0.9.

Further, the surface acoustic wave device can be used as a filter so that one of the metal films of the interdigital transducer has a positive reflection coefficient and the other has a negative reflection coefficient.

[0013]

[Operation] Positive and negative electrodes having different periods are arranged in the propagation direction,
When the film thickness of the electrode is large, the phase of excitation and the phase of reflection of the electrode can be the same phase in one propagation direction and opposite phases in the other propagation direction. If the surface acoustic wave converters having such unidirectional characteristics are arranged so that their directions face each other, a surface acoustic wave element (filter) having characteristics different in delay time depending on frequency can be obtained.

By adjusting the directivity of the surface acoustic wave converters on the excitation side and the receiving side to the same direction, a surface acoustic wave element (filter) having a constant delay time with respect to the frequency can be obtained. Particularly, in the above configuration, the third interdigital transducer has 0.2 ≦ m / p ≦ 0.7, and the fourth interdigital electrode has 0.72 ≦ m / p ≦ 0.9. For example, the fourth electrode has almost bidirectional characteristics, and a filter with low insertion loss can be obtained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 (a) is a plan view of a filter which is a surface acoustic wave element according to an embodiment of the present invention, and FIG. 1 (b) is an XY sectional view thereof. Reference numeral 1 is a piezoelectric substrate, 2 is an excitation-side surface acoustic wave converter arranged on the piezoelectric substrate 1, and 3 is a receiving-side surface acoustic wave converter arranged on the piezoelectric substrate 1. The surface acoustic wave converter 2 on the excitation side has a positive electrode 4 and a negative electrode 5 (first interdigital transducer). The surface acoustic wave converter 3 on the receiving side has a positive electrode 6 and a negative electrode 7 (second interdigital transducer). Excitation side positive electrode 4 and negative electrode 5
Are alternately arranged along the propagation direction C of the surface acoustic wave so that the electrode width m and the period p gradually become shorter. On the contrary, the positive electrode 6 and the negative electrode 7 on the receiving side are alternately arranged along the propagation direction C of the surface acoustic wave so that the electrode width m and the period p gradually increase. Here, Y-cut Z-propagation lithium niobate was used as the piezoelectric substrate 1, and aluminum films were used as the electrodes 4, 5, 6, 7. Also,
m / p = 0.5.

Graph 31 in FIG. 3 shows the relationship between m / p and insertion loss in the filter of FIG. Since the filter of FIG. 1 has symmetrical electrode arrangements on the excitation side and the reception side, graph 31 shows insertion loss characteristics in the forward direction of the surface acoustic wave converter (direction in which a surface acoustic wave having a larger amplitude is obtained). Will be shown. Graph 32 shows m / p in a filter in which the backward direction of the surface acoustic wave converter (the direction in which a surface acoustic wave having a smaller amplitude is obtained) is made to face each other contrary to FIG.
And the insertion loss. Therefore, the graph 32
Indicates the insertion loss characteristic of the surface acoustic wave converter in the backward direction. From FIG. 3, it can be seen that the insertion loss in the backward direction is larger than the insertion loss in the forward direction, and the magnitude of the insertion loss varies depending on m / p. In addition,
The advancing direction may be opposite depending on the cut and propagation of the crystal of the piezoelectric body and the type of the deposited film.

With the structure shown in FIG. 1, a filter having a bandwidth of 20% or more and an insertion loss of 5 dB or less was obtained. In the case of the configuration of FIG. 1, m / p is preferably about 0.2 to 0.7.

The example of FIG. 1 is a filter having a characteristic in which the delay time differs depending on the frequency, but in order to obtain a filter having a constant delay time with respect to the frequency, as shown in FIG. Should be aligned in the same direction. In FIG. 2, reference numeral 22 is an excitation-side surface acoustic wave converter arranged on the piezoelectric substrate, and 23 is a receiving-side surface acoustic wave converter arranged on the piezoelectric substrate. Excitation side surface acoustic wave converter 2
2 has a positive electrode 24 and a negative electrode 25 (third interdigital transducer). The surface acoustic wave converter 23 on the reception side has a positive electrode 26 and a negative electrode 27 (fourth interdigital transducer). The positive electrode 24 and the negative electrode 25 on the excitation side are alternately arranged along the propagation direction D of the surface acoustic wave so that the electrode width m and the period p gradually become shorter. Similarly, the positive electrode 26 and the negative electrode 27 on the receiving side are also alternately arranged along the propagation direction D of the surface acoustic wave so that the electrode width m and the period p gradually become shorter.

By arranging the electrodes in this way, a filter having a constant delay time with respect to the frequency was obtained.

It should be noted that one of the surface acoustic wave converters on the excitation side and the reception side is preferably one having a strong unidirectionality, and the other surface acoustic wave converter is preferably a bidirectional one having a weak unidirectionality. Therefore, from FIG. 3, one of the surface acoustic wave converters has 0.2 ≦ m.
It is preferable that /p≦0.7 and the other is about 0.72 ≦ m / p ≦ 0.9. In the filter of FIG. 2, the positive electrode 24 and the negative electrode 25 on the excitation side were set to m / p = 0.5, and the positive electrode 26 and the negative electrode 27 on the reception side were set to m / p = 0.8. As described above, a filter having a constant delay time with respect to frequency, a wide bandwidth, and a low insertion loss can be obtained.

Note that the present invention has for the first time found that the surface acoustic wave converter has directivity by positively utilizing the reflection at the electrodes arranged on the piezoelectric substrate, and the direction of the surface acoustic wave converter is determined. The surface acoustic wave device having a wide band width and a low insertion loss is formed by utilizing the characteristics. In this case, the electrode needs to have a certain thickness so that the surface acoustic wave is reflected at the electrode. Assuming that the thickness of the electrode is H and the wavelength of the surface acoustic wave is λ, 0.01 ≦
It is preferable that H / λ ≦ 0.10.

Furthermore, when Zm is the acoustic impedance of the electrode metal and Zg is the acoustic impedance of the electrode gap, the directionality of the surface acoustic wave converter is determined according to the value of Zm / Zg.

In FIG. 7, the thickness of the electrode made of Al is 200
It is a figure which shows the frequency characteristic and arrangement | positioning of an electrode for demonstrating the directivity of the chirp type transducer by an equivalent circuit analysis when it is set to 0 angstrom and Zm / Zg = 0.98. As shown in FIG. 7B, an up-chirp IDT 73 in which the arrangement density of the positive and negative electrodes is gradually increased is adjacent to the IDT (interdigital transducer, interdigital transducer) 74 having a pair of positive and negative electrodes. With this configuration, the frequency characteristic is as shown by the solid line 71 in FIG. On the contrary, as shown in FIG. 7C, a down-chirp ID in which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 76 having a pair of positive and negative electrodes.
In the configuration in which the T75s are adjacent to each other, the frequency characteristic is as shown by the broken line 72 in FIG. As for the frequency characteristic, the solid line 71 is better than the broken line 72. Therefore, I
The DT73 has the directionality shown by the arrow 73D, and the IDT75
It can be seen that has the directionality shown by the arrow 75D.

FIG. 8 is a diagram showing the frequency characteristics and the arrangement of electrodes for explaining the directivity of the chirp type transducer by the equivalent circuit analysis when Zm / Zg = 1.00. As shown in FIG. 8B, in the configuration in which the IDTs 84 having a pair of positive and negative electrodes are arranged adjacent to each other with the up-chirp IDT 83 in which the arrangement density of the positive and negative electrodes is gradually increased, The frequency characteristic is as shown by the solid line 81. Further, as shown in FIG. 8C, a down-chirp IDT in which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 86 having a pair of positive and negative electrodes.
Also in the configuration in which 85 are adjacent to each other, the solid line 8 in FIG.
The frequency characteristic shown in FIG. Therefore, it is understood that the IDT 83 and the IDT 85 have no directivity.

FIG. 9 is a diagram showing the frequency characteristics and the arrangement of electrodes for explaining the directivity of the chirp type transducer by the equivalent circuit analysis when Zm / Zg = 1.02. As shown in FIG. 9B, in the configuration in which the IDTs 93 having a pair of positive and negative electrodes are adjacent to each other with the up-chirp IDTs 93 such that the arrangement density of the positive and negative electrodes is gradually increased, The frequency characteristic is as shown by the solid line 91. On the contrary, as shown in FIG. 9C, a down-chirp IDT in which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 96 having a pair of positive and negative electrodes.
In the configuration in which 95 are adjacent to each other, the frequency characteristic is as shown by a broken line 92 in FIG. The broken line 9 shows the frequency characteristics.
2 is better than solid line 91. Therefore, the ID
It can be seen that T93 has a directionality shown by an arrow 93D and IDT95 has a directionality shown by an arrow 95D.

As a result of investigating the directivity of the chirp type transducer under various conditions as described above, in the chirp type transducer, when Zm / Zg <1, the arrangement density of the positive and negative electrodes becomes coarse to dense. It has directionality, and when Zm / Zg = 1, it has no directionality and Zm / Z
It was found that when g> 1, the arrangement density of the positive and negative electrodes has a directivity in a direction from dense to coarse. Therefore, if the filter is configured in consideration of the directivity of such a transducer, it is possible to have a low insertion loss and a wide band characteristic.

FIG. 6 shows that the thickness of the electrode made of Al is 200
It is a figure which shows the frequency characteristic and arrangement | positioning of an electrode for demonstrating the directivity of the chirp type filter by an equivalent circuit analysis at 0 angstrom and Zm / Zg = 0.98. In other words, it shows the frequency characteristics and the like in the case of configuring a filter in which the transducers used in the example of FIG. 7 are arranged. As shown in FIG. 6B, the upchirp IDT 63
With the configuration in which the IDT64 of Upchirp is adjacent to
The frequency characteristic is as shown by the solid line 61 in FIG.
On the contrary, as shown in FIG. 6C, the down chirp IDT6
In the configuration in which the No. 5 and the down-chirp IDT 66 are adjacent to each other, the frequency characteristic is as shown by the broken line 62 in FIG. The difference in the frequency characteristics is caused because the IDTs 63, 64, 65, 66 have the directivities shown by the arrows 63D, 64D, 65D, 66D, respectively, as described in FIG.

In particular, as one method, it is possible to set Zm / Zg> 1 by providing a floating electrode as shown in FIG. 10, and thereby it is possible to give directionality to the transducer. In FIG. 10, a transducer 102, which is a surface acoustic wave converter, has a positive or negative electrode 10
4,105. Furthermore, these positive and negative electrodes 10
The floating electrode 106 is provided in the gap between the electrodes 4, 106. By having the floating electrode 106, Zm / Zg of this transducer 102 became larger than 1.

In the above FIG. 2, the electrodes 24 on the excitation side,
25 is m / p = 0.5, and electrodes 26 and 27 on the reception side are m / p.
Although an example in which p = 0.8 has been described, by contrast, when the excitation side electrode has m / p = 0.25 and the reception side electrode has a double electrode structure, the filter characteristics are further improved. Figure 11
Shows an example of a filter using such a double electrode structure. In this figure, 112 is a surface acoustic wave transducer on the excitation side arranged on the piezoelectric substrate, and 113 is a surface acoustic wave transducer on the receiving side arranged on the piezoelectric substrate. The surface acoustic wave converter 112 on the excitation side has a positive electrode 114 and a negative electrode 115. This electrode has m / p = 0.25.
The surface acoustic wave converter 113 on the reception side has a positive electrode 116 and a negative electrode 117. Surface acoustic wave converter 11 on the receiving side
3 has a double electrode structure. In other words, FIG.
Of the filter of FIG. 2 is such that the electrodes 24, 25 of the filter of FIG. 2 are narrowed so that m / p = 0.25, and the electrode 26,
Electrode 11 of double electrode structure by dividing each of 27 into two
6 (116a, 116b), 117 (117a, 117
b).

Since the double electrode structure exhibits bidirectional characteristics, the characteristics are better than the structure in which the reverse direction is weakened by setting m / p = 0.8 as shown in FIG. Although the electrode width is λ / 8, it can be produced without problems at a practical frequency.

In the above embodiments, the filter was used as an example of the surface acoustic wave element for explanation, but the present invention can also be applied to a delay line. Further, the above-described unidirectional surface acoustic wave converter can be used as an impedance element itself.

[0033]

As described above, according to the present invention,
In a surface acoustic wave device in which a comb-shaped electrode having a thickness is provided on a piezoelectric or electrostrictive substrate, the phase of the electric signal by the surface acoustic wave to be excited and received and the reflection of the surface acoustic wave by the electrode in one direction Since the electrodes are arranged so that they have the same phase and opposite phases in the other direction and have a unidirectional characteristic, a surface acoustic wave element having a low insertion loss and a wide band characteristic can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view and a sectional view of a filter that is a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is a plan view of a filter in which the directions of the excitation side and the reception side are matched to each other.

FIG. 3 is a graph showing the relationship between m / p and insertion loss.

FIG. 4 is a plan view and a cross-sectional view of a filter using a conventional surface acoustic wave converter.

FIG. 5 is a plan view showing the structure of a conventional distributed delay line.

FIG. 6 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of a chirp filter with Zm / Zg = 0.98.

FIG. 7 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of a chirp transducer having Zm / Zg = 0.98.

FIG. 8 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of a chirp type transducer having Zm / Zg = 1.00.

FIG. 9 is a diagram showing frequency characteristics and arrangement of electrodes for explaining the directivity of a chirp type transducer with Zm / Zg = 1.02.

FIG. 10 is a plan view showing a transducer using a floating electrode.

FIG. 11 is a plan view showing a filter using a double electrode structure.

[Explanation of symbols]

1 ... Piezoelectric substrate, 2, 22 ... Excitation side surface acoustic wave converter, 3, 23 ... Receiving side surface acoustic wave converter, 4, 6, 2
4, 26 ... Positive electrode, 5, 7, 25, 27 ... Negative electrode.

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[Procedure amendment]

[Submission date] May 7, 1991

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 4

[Correction method] Change

[Correction content]

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

When the acoustic impedance of the metal film of the interdigital transducer is Zm and the acoustic impedance of the electrode gap is Zg, the Z of the third interdigital electrode is Z.
m / Zg is less than 1 and Z of the fourth interdigital transducer
The surface acoustic wave element can be used as a filter by setting m / Zg to be greater than 1.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 029

[Correction method] Change

[Correction content]

In particular, as one method, it is possible to adjust the value of Zm / Zg by providing a floating electrode as shown in FIG. 10, and thereby to give directionality to the transducer. In FIG. 10, a transducer 102, which is a surface acoustic wave converter, has positive or negative electrodes 104 and 105. Further, the floating electrode 106 is provided in the gap between the positive and negative electrodes 104 and 106. Every other floating electrode 106 is short-circuited. By providing such a short-circuited floating electrode 106,
The Zm / Zg of this transducer 102 was smaller than 1. Further, although not shown, by providing the floating electrode 106 opened without short-circuiting the floating electrode 106, Zm / Zg of this transducer 102 became larger than 1.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

In the above FIG. 2, the electrode 2 on the excitation side is
4 and 25 are set to m / p = 0.5, and the electrodes 26 and 27 on the reception side are set to m / p = 0.8. However, the electrodes on the excitation side are also set to m / p = 0. 5. If the electrode on the receiving side has a double electrode structure, the filter characteristics will be further improved. FIG. 11 shows an example of a filter using such a double electrode structure. In this figure, 112 is a surface acoustic wave transducer on the excitation side arranged on the piezoelectric substrate, and 113 is a surface acoustic wave transducer on the receiving side arranged on the piezoelectric substrate. The surface acoustic wave converter 112 on the excitation side has a positive electrode 114 and a negative electrode 115. This electrode has m / p = 0.5
Is. The surface acoustic wave converter 113 on the receiving side is the positive electrode 11
6 and negative electrode 117. The surface acoustic wave converter 113 on the receiving side has a double electrode structure. In other words, the filter of FIG. 11 has the electrodes 24, 2 of the filter of FIG.
5 is left as it is, and each one of the electrodes 26 and 27 is set to 2
The electrodes 116 (116a, 11a) having a double electrode structure are divided.
6b), 117 (117a, 117b). In this case, m / p = 0.25 for the table electrode.
Becomes

[Procedure correction 6]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 11

[Correction method] Change

[Correction content]

FIG. 11 ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 5, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

Further, in the distributed delay line as shown in FIG. 5, the delay time of a high frequency signal is long, and the delay time of a low frequency signal is a short down chirp delay line, and an up chirp delay line having the opposite characteristic. You can also get However, also in this case, the conventional distributed converter, that is, the converter having the bidirectional characteristic is used, and the converter is not a low insertion loss converter.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction content]

FIG. 7 shows that the thickness of the electrode made of Al is 2
It is a figure which shows the frequency characteristic and arrangement | positioning of an electrode for demonstrating the directivity of the chirp type transducer by the equivalent channel analysis at 000 angstrom and Zm / Zg = 0.98. As shown in FIG. 7B, a down-chirp IDT 7 in which the arrangement density of the positive and negative electrodes gradually increases toward the IDT (interdigital transducer, interdigital transducer) 74 having a pair of positive and negative electrodes.
In the configuration in which 3 are adjacent to each other, the frequency characteristic is as shown by the solid line 71 in FIG. On the contrary, as shown in FIG.
In the configuration in which the IDTs 75 having a pair of positive and negative electrodes are adjacent to the IDTs 75 of up-chirp so that the arrangement density of the positive and negative electrodes becomes gradually rough, the frequency characteristics as shown by the broken line 72 in FIG. Become. As for the frequency characteristic, the solid line 71 is better than the broken line 72. Therefore, the IDT 73 has the direction shown by the arrow 73D, and the ID
It can be seen that T75 has the directionality shown by the arrow 75D.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

FIG. 8 is a diagram showing a frequency characteristic and an arrangement of electrodes for explaining the directivity of the chirp type transducer by an equivalent circuit analysis when Zm / Zg = 1.00. As shown in FIG. 8B, in a configuration in which the IDTs 83 having a pair of positive and negative electrodes are adjacent to each other with the down-chirp IDTs 83 so that the density of the arrangement of the positive and negative electrodes is gradually increased, the configuration shown in FIG. The frequency characteristic is as shown by the solid line 81. Further, as shown in FIG. 8C, an up-chirp I in which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 86 having a pair of positive and negative electrodes.
Even with the configuration in which the DTs 85 are adjacent to each other, the frequency characteristic shown by the solid line 81 in FIG. Therefore, IDT8
It can be seen that both 3 and IDT85 have no directivity.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

FIG. 9 is a diagram showing the frequency characteristics and the arrangement of electrodes for explaining the directivity of the chirp transducer by the equivalent circuit analysis when Zm / Zg = 1.02. As shown in FIG. 9B, in the configuration in which the down-chirp IDT 93 in which the arrangement density of the positive and negative electrodes is gradually increased toward the IDT 94 having the pair of positive and negative electrodes is adjacent, The frequency characteristic is as shown by the solid line 91. On the contrary, as shown in FIG. 9C, the up-chirp I of which the arrangement density of the positive and negative electrodes gradually becomes coarser toward the IDT 96 having the pair of positive and negative electrodes.
In the configuration in which the DTs 95 are adjacent to each other, the broken line 92 in FIG.
The frequency characteristics are as shown in. Regarding the frequency characteristic, the broken line 92 is better than the solid line 91. Therefore,
The IDT 93 has the direction shown by the arrow 93D, and
It can be seen that 5 has the directionality shown by the arrow 95D.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

FIG. 6 shows that the thickness of the electrode made of Al is 2
It is a figure which shows the frequency characteristic and arrangement | positioning of an electrode for demonstrating the directivity of the chirp type filter by an equivalent circuit analysis at 000 angstrom and Zm / Zg = 0.98. In other words, it shows the frequency characteristics and the like in the case of configuring a filter in which the transducers used in the example of FIG. 7 are arranged. As shown in FIG. 6 (b), down chirp IDT
In the configuration in which 63 and the down-chirp IDT 64 are adjacent to each other, the frequency characteristic is as shown by the solid line 61 in FIG. On the contrary, as shown in FIG. 6C, the ID of the up chirp
In the configuration in which the T65 and the up-chirp IDT 66 are adjacent to each other, the frequency characteristic is as shown by the broken line 62 in FIG. The difference in the frequency characteristics is caused because the IDTs 63, 64, 65, 66 have the directivities shown by the arrows 63D, 64D, 65D, 66D, respectively, as described in FIG.

[Procedure Amendment 7]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

[Procedure Amendment 8]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

[Figure 7]

[Procedure Amendment 9]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

[Procedure Amendment 10]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Change

[Correction content]

[Figure 9]

Claims (4)

[Claims] 1. A surface acoustic wave device comprising a piezoelectric or electrostrictive substrate on which a comb-shaped electrode having a thickness is provided. Positive and negative electrodes whose electrode width and period are gradually reduced in the propagation direction of the surface acoustic wave. A first interdigital transducer that excites alternating surface acoustic waves and a second surface acoustic wave that alternately arranges positive and negative electrodes whose electrode width and period gradually increase in the propagation direction of the surface acoustic wave. A surface acoustic wave device comprising: a comb-shaped electrode. 2. A surface acoustic wave device comprising a piezoelectric or electrostrictive substrate provided with thick interdigital electrodes, in which positive and negative electrodes whose electrode width and period are gradually shortened in the surface acoustic wave propagation direction are provided. A third interdigital transducer for exciting surface acoustic waves alternately arranged and a fourth surface for receiving surface acoustic waves in which positive and negative electrodes whose electrode width and period are gradually shortened in the propagation direction of the surface acoustic wave are alternately arranged. A surface acoustic wave device comprising: a comb-shaped electrode. 3. When the electrode width of the interdigital transducer is m and the period is p, the third interdigital electrode is 0.2 ≦ m.
/P≦0.7, and the fourth interdigital electrode is 0.7
The surface acoustic wave device according to claim 2, wherein 2 ≦ m / p ≦ 0.9. 4. The filter using the surface acoustic wave device according to claim 2, wherein the reflection coefficient of the metal film of the interdigital transducer is greater than 1 at one interdigital electrode and less than 1 at the other interdigital electrode. .